Varying velocity gearing

ABSTRACT

Gearing, more particularly apparatus for producing different straight line, or rotary, continuous, or periodical motions of uniform, or varying velocity. The apparatus comprises a first, axially moving gear element on a driving shaft, said first gear element meshing with another, second gear element on a driven shaft. The first gear is preferably a worm or a helical gear with teeth disposed at an angle with respect to the axis of the driving shaft. Said axially movable first gear element is preferably equipped with a cam meshing with a cam follower which is stationary with respect to the housing of the apparatus. The axially movable first gear element may also be reciprocated by a crank drive or an eccentric mechanism.

United States Patent [1 1 Sarls VARYING VELOCITY GEARING [75] Inventor: Agoston Sarls, Budapest, Hungary [73] Assignee: Lampart, Budapest, Hungary [22] Filed: Mar. 29, 1973 211 App]. No.: 345,989

Primary ExaminerLeonard H. Gerin 5] June 28, 1974 5 ABSTRACT Gearing, more particularly apparatus for producing different straight line, or rotary, continuous, or periodical motions of uniform, or varying velocity. The apparatus comprises a first, axially moving gear element on a driving shaft, said first gear element meshing with another, second gear element on a driven shaft. The first gear is preferably a worm or a helical gear with teeth disposed at an angle with respect to the axis of the driving shaft. Said axially movable first gear element is preferably equipped with a cam meshing with a cam follower which is stationary with respect to the housing of the apparatus. The axially movable first gear element may also be reciprocated by a crank drive or an eccentric mechanism.

5 Claims, 4 Drawing Figures PATENTEDJUNZB m4 3.820.410

SHEET 2 0F 3 11 l l I 'VARYING VELOCITY GEARING The present invention relates to an apparatus for producing different straight line or rotary, continuous or periodic motions of uniform or varying velocity.

It is well-known in machine engineering to actuate machines and equipments by drives producing intermittent motions. The known drives of the art are Geneva-type gearings, ratchet mechanisms, clutches running free in one direction, or various cam drives. The main drawback of these devices is that they are not suitable .for the production of quick movements, because the transmitted movements are accompanied by harmful phenomena vibrations, impacts, noises, etc., and the working life of the driven equipment is low. A suitable machine life can be achieved only with drives of low power.

Among the above-mentioned drives, the free running clutches ensure a relatively good movement, but, being friction clutches, they have the drawback of slippage, i.e. they do not ensure a positive connection between the driving and the driven part.

As is well-known, principally the best dynamic motions can be achieved with cam drives, because cam paths may be designed according to the laws of motions ensuring the best dynamic properties. In practice, however, these dynamic properties could be effective only in the case of paths of great displacements and small pressure angles. There may also be found in machine industry guide discs of relatively small diameter having cam lobes on their circumference. In such discs the curves of the cams are necessarily formed on a very small arc, i.e., a 360/60 6 central angle. With such small arcs, as is well-known, greater movements may be obtained only with higher values of the pressure angle.

. There must often be considered the phenomenon of undercuttings.

As to other cam drives, altemate path mechanisms are also known for actuating circular tables of single purpose milling and processing machines. An alternate path mechanism transforms the rotary motion of an input shaft of constant speed into an arbitrary rotary movement (or indirectly into other motions, too) of the output shaft. That movement is periodic, but one period may comprise several accelerating, decelerating or constant speed sections. Such a device may be expediently used for actuating cam discs. lts advantage is that the disc may move with varying speed or even stay for a time, while the input shaft rotates. Production of useful sections may be carried out more favorably as sections on the disc which ensure standstill positions of the controlled parts are not required.

Such a solution may be found, for instance, in the book of G. A. Schaumjan: Automaten (VEB Verlag Technik, Berlin 1961, Page 462, FIG. 6/79g). These devices comprise an alternate path with one working and one stationary position arranged on the whole circumference of the guiding member, said guiding member effecting indexing of the circular table. This equipment with usual dimensions conforms with the principle, mentioned above, according to which application of laws of movement with good dynamic characteristics give good practical results when relatively great displacements can be achieved by small pressure angles. The cam curve of the alternate path, however, approaches in vain the optimal conditions, if the machine, due to the applied principle of indexing, is subjected to of the control curve cannot be manufactured with absolute precision, and the error of height elevation grows with abrasion during service. Elevation of the control curve and pitches of the rolls do not correspond because of the reasons cited above. Therefore due to elastic deformation, a high overstress arises by overshoots of the engaging rolls at abrupt startings and stoppings. This overstress may be a multiple of the maximal load in service.

The conventional alternate path mechanism therefore does not work satisfactorily at speeds exceeding 25 to 30r.p.m. (Gep 1968/12, Pages 509-516). By a cer tain correction of traditional path curves, a so-called combined path curve may be formed (Gep 1970/2, Pages 59-65) having a dynamic factor 30% lower than the former. This enables a small increase in acceleration; nevertheless the alternate path mechanism equipped even with the combined path curve is not altogether satisfactory.

The present invention has among its objects the provision of a drive mechanism exempt from the above disadvantages of drives producing periodical motions, but ensuring their advantages and by the use of which performance and machine life can be increased.

The drive according to the present invention comprises an axially moving element on the driving shaft, said element actuating another element on said shaft fixed in the direction of rotation, but slidable axially, preferably a worm or a helical gear with teeth including an angle with the direction of sliding.

Said moving element is preferably equipped with a cam meshing by a feeler stationary with respect to the housing.

The moving element may also be a device performing reciprocating motion, as e.g., a crank drive or an eccentric mechanism.

The invention will be illustrated in detail by way of examples and the drawings.

FIG. 1 shows a detail in elevation of a prior art cam disc;

FIG. 2 is a schematic view in perspective of a first embodiment of the invention;

FIG. 3 is aschematic view in perspective of a second embodiment of the invention; and

FIG. 4 is a fragmentary viewof an eccentric disc having a periphery in the form of an Archimedean spiral which can be employed with the apparatus of the invention.

FIG. 1 well illustrates the fact that the arc having a central angle (1) may be only partly utilized, because incurvations are formed on the starting and finishing section of path elevation h, for dynamic reasons on the one hand, and for geometrical reasons on the other hand. Only a small part of the radial displacement h takes place on the arcs corresponding to angles a and B which are great enough with respect to the central angle The disc according to FIG. 1 therefore does not carry out any useful work at the arcs corresponding to angles a and B. The situation is similar on the arc sections corresponding to angle y corresponding to the position of rest.

In the embodiment of the invention shown in FIG. 2, on a driving shaft 1 a worm 2 integrally secured to a control drum 3 is slidably mounted for movement in an axial direction[ The worm 2 and cam 3 are splined to the shaft 1 so as to rotate therewith. The control drum 3 has a barrel cam 4 which meshes with a cam follower 5 fixed on the machine frame. In the course of rotation of shaft 1 with respect to the fixed cam follower 5 the control drum 3 moves together with the worm 2. This displacement modifies the worm gear ratio which is determined by the pitch of the worm. On one section of cam 4, for example, the pitch of the cam path may conform with the pitch of worm 2 but have an opposite direction of inclination. When the cam follower 5 is engaged on this section of cam 4, the worm wheel 7 which and stops gently without impact. This action is repeated at every revolution of driving shaft 1.

In the embodiment of the apparatus shown in FIG. 3, parts which are the same as or similar to those in FIG. 2 are designated by the same reference characters with an added prime In such embodiment, the driving shaft 1' is shown driven by a chain and sprocket at one end thereof, as in FIG. 2. The angular speed of the driven shaft 6' is varied by axially sliding the integral worm 2' and spool 3' axially of the shaft 1, whereby to vary the speed of the worm gear 7 which meshes with the worm 2'. The driven shaft 6 has affixed thereto a sprocket 8 which drives a second sprocket 19 through the medium of a chain 18. Sprocket 19 is affixed to a second driven shaft 20 journalled in the housing of the apparatus, as shown. The element 18, instead of being a chain, may be a timing" belt, and the elements 8 and 19 may be cogged wheels over which the timing belt is entrained.

The driving shaft 1' drives a further vertical shaft 9 through-the medium of meshing bevel gears 10, 10. Affixed to the shaft 9 is an eccentric 11 having a circular cylindrical periphery, there being a ring or strap 12 which encircles the eccentric 11 and is fixedly connected to a reciprocable rod 13. Connected to the rod 13 through a hinged joint 14 is a second rod 15 having a bent, vertically disposed portion 16 provided with a shoe which accurately engages an annular transverse recess 17 in the spool portion 3. It will be apparent that upon the driving of the shaft 1 and thus the shaft 9, the parts 13, 14, 15, and 16 reciprocate through a path which has a length equal to twice the eccentricity contains only one section of motion and one section of rest, similarly to the above-described alternate path mechanisms.

The embodiment of the apparatus shown in FIG. 3 may be modified by substituting for the circular cylindrical eccentric 11 and the ring 12 an Archimedean spiral cam 21, shown in FIG. 4, and a cam follower cooperating therewith, there being means such as a spring which causes the cam follower to be in constant engagement with the surface of the cam. With such arrangement there is produced periodic movement of the member 2', 3, the originally necessary arcs corresponding to angles a B, and 7 shown in connection with the cam in FIG. 1 being unnecessary for the drive according to the present invention. By use of such Archimedean spiral cam 21 the pressure angles are made more favorable, the manufacture of the cam is simplified, manufacturing errors are reduced and dynamic over-stresses arising from them are diminished.

With theconstruction described immediately above, with a control disc of Archimedean spiral form or of other simple curved form a control disc having a diameter equal to that of the eccentric 11 in FIG. 3 and having equal pressure angle may contain twice as many cams or eccentrics as the member 11.

The apparatus in accordance with the invention may be used without any modification for replacement of speed-changing gears previously known in machine industry, and also in apparatus of greater sizes and powers. The changing speed motion is achieved by forming the section of cam 4 (FIG. 2) of control drum 3, the pitch of cam 4 being at every part smaller than the pitch of worm 2. In this case the control drum 3 modifies the drive resulting from'the pitch of worm 2 so that within one revolution of driving shaft 1 the motion of the driven shaft 6 is, in one section, at a slower speed, and in the other section of the cam at a higher speed.

In another, unillustrated embodiment of the invention the path of the cam 4 in the control drum 3 may be formed, while retaining its favorable dynamic properties, so that in one portion of each revolution of driving shaft 1 the driven shaft 6 is driven in a first direction, and in another portion of said one revolution of shaft 1 the shaft 6 is driven in the reverse direction.

Favorable operating characteristics of the driving apparatus in accordance with the invention are ensured by having the driving and driven members continually engaged. The worm to worm wheel gearing of the invention is not sensitive to errors of pitch, and thus can use parts with greater tolerances of manufacture. Changes in pitch of the controlling parts change the relation between the moving and at rest portions of the periodic motion only to a negligible degree, which may, for instance, be on the order of 0.0l percent.

Corrections in the path are not needed because of the worm gearing, and also overshooting of the control does not cause problems. Thus in the course of operation of the gearing according to the invention, no dynamic overstresses of any kind arise between the individual sections of the variable motion. The apparatus of the invention have motions with dynamic properties which are superior to those of the above-described known cam devices and known alternate path mechanisms. A further advantage of the equipment according to the invention, compared with the above-described alternate path mechanisms, is that it can be produced with significantly smaller directions and in every respect can be made more economically.

It is to be understood that in accordance with the invention the driven shaft 1 may be driven at either a constant or a variable speed by respective known rotating driving mechanisms. It is also to be understood that two or more driving mechanisms in accordance with the invention may be connected in series, that is, the ultimate driven shaft of one such mechanism may be connected to drive the driving shaft 1 or 1' of the next mechanism in accordance with the invention.

Although the invention is illustrated and described with reference to a plurality of preferred embodiments thereof, it is to be understood that it is in no way limited by the disclosure of such a plurality of embodiments, but is capable of numerous modifications within the scope of the appended claims.

What is claimed is:

1. Gearing comprising a driving shaft, means to rotate the driving shaft, a first element for positive coupling mounted on the driving shaft for rotation therewith and for sliding therealong, a driven shaft, a second element for positive coupling with said first element affixed to the second shaft and disposed in constant mesh with the first element along the driving shaft, whereby periodically to vary the ratio of the speeds of rotation of the driving shaft and the driven shaft.

2. Gearing according to claim I, wherein the first and second elements for positive coupling are gears having teeth desposed at an angle to the axis of the driving shaft.

3. Gearing according to claim 1, wherein the first element is a worm, and the second element is a worm wheel.

4. Gearing according to claim 1, wherein the means for reciprocating the first element comprises a cam affixed to the first element, and a fixed cam follower engaging said cam.

5. Gearing according to claim 1, wherein the means for reciprocating the first element comprises an eccentric member driven. by the driving shaft, an eccentric following member, and means drivingly connecting the eccentric following member to the first element. 

1. Gearing comprising a driving shaft, means to rotate the driving shaft, a first element for positive coupling mounted on the driving shaft for rotation therewith and for sliding therealong, a driven shaft, a second element for positive coupling with said first element affixed to the second shaft and disposed in constant mesh with the first element along the driving shaft, whereby periodically to vary the ratio of the speeds of rotation of the driving shaft and the driven shaft.
 2. Gearing according to claim 1, wherein the first and second elements for positive coupling are gears having teeth desposed at an angle to the axis of the driving shaft.
 3. Gearing according to claim 1, wherein the first element is a worm, and the second element is a worm wheel.
 4. Gearing according to claim 1, wherein the means for reciprocating the first element comprises a cam affixed to the first element, and a fixed cam follower engaging said cam.
 5. Gearing according to claim 1, wherein the means for reciprocating the first element comprises an eccentric member driven by the driving shaft, an eccentric following member, and means drivingly connecting the eccentric following member to the first element. 